The Certus does have a following here.

Her's a thread on Ash's 450:

http://forums.nitroexpress.com/showflat....rt=all&vc=1

I wonder if the barrel was originally a 450/400 barrel and was rebored and reproofed to the light cordite 450 load.
Looks really thin with a LOT of taper at the breech.
Anybody here know what the original Certus proof load was for the 400?